Taxol, which is useful as a therapeutic agent for ovarian cancer, mammary cancer, lung cancer and the like, is a taxane-type diterpene identified after being isolated from Taxus brevifolia NUTT, which is a plant belonging to genus Taxus, family Taxaceae and has a complex ester group which is related to its activity. Taxol can be found in all the parts of the plant body of Taxus brevifolia NUTT, but the bark has been reported to exceed all others in its content of the taxol. At present, taxol is collected from a natural or a cultivated plant body, however, the plant belonging to genus Taxus grows slowly, and it takes more than 10 years to grow to a height of 20 cm above the ground, besides the tree dies after its bark is taken off, thus it has been difficult to easily obtain a large amount of taxol. It would be advantageous if a taxane-type diterpene such as taxol and baccatin III which is a precursor of taxol, can be produced by the use of tissue culture, since a large amount of taxol can be easily obtained without cutting down the trees.
As a conventional method of producing taxol by utilizing cultured plant cells, a US patent was issued on a production method utilizing cultured cells of Taxus brevifolia NUTT (U.S. Pat. No. 5,019,504), however, the yield of taxol production described therein is 1-3 mg/l, and that is insufficient for the industrial production. Besides, the production of taxol by the cell culture is unstable and even when a primary cell of high productivity can be obtained by selection, it is difficult to keep its content by subculturing [E. R. M. Wickremesine et al., World Congress on Cell and Tissue Culture (1992)].
On the other hand, as a prior art in the taxol production, a semisynthetic method from baccatin III, which is a precursor in biosynthesis of taxol, is disclosed in the specification of U.S. Pat. No. 5,015,744 issued to Holton et al. By the use of the plant tissue culture, a raw material for the semisynthetic process such as baccatin III can be produced, thus the plant tissue culture can be also utilized for taxol production by the above-mentioned semisynthetic process.